With the increasing use of hyperthermia in the clinic, there has been an interest in cellular response of cells to hyperthermia. Hyperthermia induces a transient thermoresistant state, thermotolerance, which has been demonstrated both in-vivo and in-vitro. An understanding of thermotolerance is a challenge for the design of efficacious fractionated hyperthermia protocols. The objective of the proposed research is to investigate the molecular mechanisms involved in thermotolerance. More specifically, we wish to determine whether or not the thermotolerant state is associated with an ameliorated ability to recover from heat-induced damage in cellular processes and whether a specific heat shock protein, the hsp 70 plays a role in this process. We propose to test this hypothesis by examining heat-induced disruptions of ribosomal RNA metabolism and their recovery in cells displaying various thermal behavior. We will characterize heat-induced disruptions in ribosomal RNA metabolism, including alterations in its synthesis and processing, alterations in the proteins content and phosphorylation of the nucleolus, and their recovery in cells displaying various thermal behaviors in normal, thermotolerant and permanently heat-resistant cells. We will also examine these processes in an in-vitro/in-vivo tumor system and in mammalian cell lines with different intrinsic heat sensitivities. The role of hsp 70 will be examined by comparing these processes in cells which contain various levels of hsp 70, including thermotolerant cells induced by various methods and in permanently heat resistant cells expressing elevated levels of hsp 70. We also propose to perform microinjection experiments to examine the role of hsp 70 in rRNA metabolism directly. These studies will delineate molecular mechanisms of thermotolerance in both in vivo and in vitro which could eventually be utilized to differentially alter the thermal response of normal and tumor tissues. Moreover, they will test for a specific function associated with hsp 70 and possibly generate biochemical tests for thermotolerance and intrinsic heat resistance in the clinic.